'Bionic eye' may help reverse blindness

A "bionic eye" may one day help blind people see again, according to US researchers who have successfully tested the system in rats.

The eye implant - a 3-millimetre-wide chip that would fit behind the retina - could be a dramatic step above currently available technology, says the team at Stanford University, California, US.

About 1.5 million people worldwide have a disease called retinitis pigmentosa, and 700,000 people in the western world are diagnosed with age-related macular degeneration each year. In both degenerative diseases, retinal cells at the back of the eye that process light gradually die.

Groups at the University of Southern California and the University of Illinois at Chicago Medical Center, both in the US, have developed retinal implants for humans to improve these conditions. But Daniel Palanker, a physicist at Stanford working on the bionic eye, says these implants have very low resolution.

"Basically, [that work is] a proof of principle," Palanker says. He claims his system has higher resolution.

A visual acuity of 20/20 is considered normal, while 20/400 is considered blind. Palanker and his team say their device could provide acuity of 20/80. "With 20/80 vision you can certainly read large forms and live independently," Palanker says. "It's a huge step forward."

Wireless transmission

For the device to work, the microchip would have to be implanted behind the retina of the blind person. The patient would wear goggles mounted with a small video camera. Light enters the camera, which then sends the image to a wireless wallet-sized computer for processing. The computer transmits this information to an infrared LED screen on the goggles.

The goggles reflect an infrared image into the eye and on to the retinal chip, stimulating photodiodes on the chip. The photodiodes mimic the retinal cells by converting light into electrical signals, which are then transmitted by cells in the inner retina via nerve pulses to the brain.

The goggles are transparent so if the user still has some vision, they can match that with the new information - the device would cover about 10° of the wearer's field of vision.

Living-cell movement

In the rat study, Palanker showed that by placing the implant behind the retina, the remaining living retinal cells moved closer to the photodiodes on the implant The closer the cells get to the array, the better the resolution of the image. Palanker says that his goal is for there to be no more than 10 microns of space between the retinal cells and the implant, equivalent to the width of just one cell.

When the implants were used in blind rats, the rodents appeared to have some restored vision. Rats with the retinal implants passed a vision test by responding to having a pattern of black and white stripes waved in front of them.

Before the device can be stepped up to humans, Palanker says the team will have to trial larger implants in bigger animals and conduct more safety tests.

The study was partly funded by the US Air Force and VISX Corp, a company based in California, US.

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